The present invention relates to a method and device for treating an oil sludge and an oil-contained waste water which are generated in the process of transportation, refining, storage or usage of petroleum.
Generally, industrial waste treating companies are entrusted to treat an oil tank sludge or a crude oil tanker sludge from oil refining companies in oil producing countries or oil consuming countries, an engine oil from machine repairing shops, and a transformer oil from power distributing companies. If such an oil sludge is incinerated, a harmful gas such as SOx, NOx and COx is diffused in the atmosphere to cause acid rain which will damage forest and also cause photochemical smog which will lead to infant asthma.
If the oil sludge is thrown away in the ground, a light oil contained in the oil sludge is vaporized by a solar heat and a ground heat (in case of desert or soil), and is diffused in the atmosphere to cause photochemical smog. On the other hand, a heavy oil contained in the oil sludge is penetrated into the ground together with rain water to cause soil pollution in a wide area. Further, the heavy oil flows into a ground water to cause pollution of the ground water.
The oil in the oil sludge can be recovered by separating the same from the water in the oil sludge. However, a process of separating the oil from the water in the form of an emulsion is difficult to conduct.
The present inventor has already proposed a sewage treating method and device as mentioned below.
In Japanese Patent Laid-open Publication No. 48-59658, a sewage such as domestic drainage is adjusted to pH (hydrogen ion concentration) 7.0.+-.0.5, and is then filtered by zeolite to remove color, odor and metal. In electrolyzing the pH adjusted liquid, aluminum is used for anode and cathode, and the polarity of both the electrodes is changed to prevent deposition of metal hydroxide onto the electrodes and thereby accelerate the electrolysis.
In Japanese Patent Laid-open Publication No. 49-32462, a sewage is sprayed to contact a blowing purified air, thereby separating oil from the sewage and oxidatively deodorizing the same. Then, pH of the sewage is adjusted to 5.5-7.0. Thereafter, the sewage is fed to a plurality of electrolytic cells communicated with each other to conduct electrolysis by using aluminum as anode and cathode as changing the polarity of both the electrodes.
Thus, the sewage such as industrial drainage and domestic drainage can be treated by the above sewage treating method and device. However, the oil sludge containing 30% or more of heavy oil cannot be treated.
Accordingly, there is a problem that the pollution of the atmosphere and the ground water cannot be prevented by the above conventional treating method and device.